In modern combustion engines, to prevent the unregulated passage of lubricating oil through the guide slot towards the valve seat, the valve shafts of the combustion engine are sealed on the valve drive side. The seals for the valve shafts function initially to block the oil coming from the valve drive so that the oil is prevented from entering the valve guide slot. It is necessary to prevent excess stripping because otherwise, in the absence of sufficient lubrication, high wear can occur on the valve shaft and guide. Valve shaft seals thus also function as oil metering devices.
Known seals for valve shafts in combustion engines consist of a sealing element fabricated of an elastomer material. The sealing element is provided with a spring-loaded sealing lip having a sealing edge that rests in a sealing manner on the valve shaft. The sealing edge is formed by two surfaces of the sealing lip which have a frustum shape and are angled relative to each other. The sealing lip strips the oil discharged from the valve chamber during reciprocation. By varying the spring preload and the sealing lip design, it is possible to reduce the oil passage at the valves to the small amount required for lubrication. In this way, the most useful amount for each motor is achieved. An important characteristic of the seal is the angle of the surface of the sealing edge that faces the valve chamber. In most cases, this angle .alpha. has a value of 40.degree. to 45.degree. relative to the axis of the valve shaft. Even smaller angles up to 30.degree. have been used for special applications.
The metering of oil for valve shaft sealing rings, particularly in the case of sealing ring designs with a shallow angle .alpha., is strongly influenced by the oil supply at the valve. However, the oil supply varies from valve to valve because of the construction of the cylinder head, particularly the position of the inflow bore. The oil supply from valve to valve also varies because of the oil pump drive, also determined by the load point of the motor.
Particularly in the case of valve shaft sealing rings designed with a small contact angle (.alpha.&lt;35.degree.), a gap that greatly tapers off is present on the oil side of the sealing ring. Thus, depending on the oil supply, a dynamic pressure is generated when the valve opens, and this influences the amount of oil passing through the valve. This phenomenon is rarely known to occur in standard valve shaft sealing rings having contact angles .alpha. greater than 40.degree..
In light of the foregoing, a need exists for a valve shaft sealing ring in which, independently from the oil supply, the same dynamic pressure is substantially always present in the tapering gap in front of the sealing edge, while excess oil is stripped.